New insights into plant responses to the attack from insect herbivores

Blooming resilience: transcriptomic insights into cotton flower responses to boll weevil infestation

KEY MESSAGE

Cotton plants undergo a drastic transcriptional reprogramming after cotton boll weevil infestation, modulating several defense pathways to cope with the damage. The global demand for cotton fiber continues to rise, but pests and pathogens significantly hinder cotton production, causing substantial losses. Among these, the cotton boll weevil (Anthonomus grandis) is one of the most destructive pests. To investigate the molecular responses of cotton (Gossypium hirsutum) to boll weevil infestation, we evaluated the global gene expression of floral buds using mRNA-seq. Additionally, we analyzed the expression of non-coding RNAs, including microRNAs (miRNAs) and long intergenic non-coding RNAs (lincRNAs). Infestation by cotton boll weevil larvae triggered a rapid and drastic transcriptional reprogramming, with 1,656 and 1.698 genes modulated after two and twelve hours, respectively. Gene ontology enrichment analysis revealed significant regulation of defense-related and developmental processes, including photosynthesis, primary metabolism, and cell organization. Transcription factor families such as ERF, WRKY, GRAS, and NAC were strongly affected, highlighting their roles in coordinating defense responses. The jasmonate pathway showed intensive modulation, alongside secondary metabolite pathways like terpenoids and phenylpropanoids, which contribute to plant defense mechanisms. Non-coding RNAs also played a critical role in the response. We identified 921 unique known and novel miRNAs, with 36 modulated by the infestation, and predicted 98,850 putative lincRNAs, several of which were differentially expressed. Understanding the genetic and molecular mechanisms underlying cotton's defense against boll weevil, particularly during early infestation stages, is vital for developing biotechnological strategies to reduce pest damage. Our findings provide critical insights to enhance cotton resilience against herbivores.

Regulatory mechanisms of nitrogen homeostasis in insect growth and development

Nitrogen is an essential element for the synthesis of proteins, nucleic acids, and various other critical biological molecules in insects. The maintenance of nitrogen homeostasis in insects is achieved through a balance of dietary intake, metabolic conversion, and excretion. Insects primarily acquire nitrogen from their diet, which is subsequently metabolized into amino acids, proteins, and other vital biomolecules following digestion and absorption. Excess nitrogen is excreted in forms such as uric acid, allantoin, allantoic acid, urea, and ammonia. Disruptions in nitrogen regulation can result in ammonia toxicity and abnormal production or excretion of nitrogenous metabolites, including uric acid, ultimately impairing insect development and survival. This review examines the mechanisms underlying nitrogen homeostasis in insects, with a focus on the intricate regulatory roles of carbohydrate metabolism, amino acid metabolism, uric acid metabolism, urea and polyamine metabolism, ammonia transport pathways, and symbiotic interactions. By elucidating these processes, this review aims to enhance our understanding of insect nutritional metabolism and developmental biology, while offering novel perspectives for the development of more effective pest management strategies.

Integrative transcriptome and metabolome analysis uncovers the Toxoptera aurantii (Hemiptera: Aphididae) response of two Camellia sinensis (Ericales: Theaceae) cultivars

The tea aphid Toxoptera aurantii Boyer (Hemiptera: Aphididae) is a destructive pest that infests tea plants. The resistance mechanisms of the tea plant against T. aurantii infestation are largely unexplored. This study investigates the defensive response of tea plants to T. aurantii feeding using an aphid-resistant Camellia sinensis cultivar 'Qiancha1' (QC1) and an aphid-susceptible C. sinensis cultivar 'Huangjinya' (HJY). Transcriptomics and metabolomics analyses were conducted on 4 samples: QCCK (T. aurantii non-infested QC1), HJYCK (T. aurantii non-infested HJY), QC24 (T. aurantii-infested QC1 for 24 h), and HJY24 (T. aurantii-infested HJY for 24 h). The results showed that the differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) in the 2 comparison groups (QCCK vs. QC24 and HJYCK vs. HJY24) were primarily enriched in metabolic pathways, including hormone signal transduction, phenylpropanoid biosynthesis and flavonoid biosynthesis. Following aphid infestation, the resistant cultivar QC1 exhibited more DEGs and DAMs than the susceptible cultivar HJY, indicating a stronger response to T. aurantii feeding stress. Additionally, the expression of phenylpropanoid- and flavonoid-related genes (CYP, 4CL, FLS, F3H, and LAR) was significantly upregulated in the resistant cultivar QC1 compared with that in the susceptible cultivar HJY. Metabolites involved in phenylpropanoid/flavonoid pathways, such as p-coumaroyl-CoA, caffeoylquinic acid, and feruloyl-CoA, were exclusively induced in QC1. These findings suggest that phenylpropanoid/flavonoid pathways play pivotal roles in tea plant resistance to T. aurantii infestation, providing valuable insights for the breeding and utilization of resistant germplasms.

Impact of Ectropis grisescens Warren (Lepidoptera: Geometridae) Infestation on the Tea Plant Rhizosphere Microbiome and Its Potential for Enhanced Biocontrol and Plant Health Management

The root-associated microbiome significantly influences plant health and pest resistance, yet the temporal dynamics of its compositional and functional change in response to Ectropis grisescens Warren (Lepidoptera: Geometridae) infestation remain largely unexplored. The study took samples of leaves, roots, and rhizosphere soil at different times after the plants were attacked by E. grisescens. These samples were analyzed using transcriptomic and high-throughput sequencing of 16S rRNA techniques. The goal was to understand how the plant's defense mechanisms and the microbial community around the roots changed after the attack. Additionally, bacterial feedback assays were conducted to evaluate the effects of selected microbial strains on plant growth and pest defense responses. By conducting 16S rRNA sequencing on the collected soil samples, we found significant shifts in bacterial communities by the seventh day, suggesting a lag in community adaptation. Transcriptomic analysis revealed that E. grisescens attack induced reprogramming of the tea root transcriptome, upregulating genes related to defensive pathways such as phenylpropanoid and flavonoid biosynthesis. Metagenomic data indicated functional changes in the rhizosphere microbiome, with enrichment in genes linked to metabolic pathways and nitrogen cycling. Network analysis showed a reorganization of core microbial members, favoring nitrogen-fixing bacteria like Burkholderia species. Bacterial feedback assays confirmed that selected strains, notably Burkholderia cepacia strain ABC4 (T1) and a nine-strain consortium (T5), enhanced plant growth and defense responses, including elevated levels of flavonoids, polyphenols, caffeine, jasmonic acid, and increased peroxidase (POD) and superoxide dismutase (SOD) activities. This study emphasizes the potential of utilizing root-associated microbial communities for sustainable pest management in tea cultivation, thereby enhancing resilience in tea crops while maintaining ecosystem balance.

Genome-Wide Identification of the Defensin Gene Family in Triticum durum and Assessment of Its Response to Environmental Stresses

Plant defensins (PDFs) are a group of cationic antimicrobial peptides that are distinguished by their unique tertiary structure and play significant roles in physiological metabolism, growth, and stress tolerance. Defensins are key components of plant innate immunity; they can target a wide variety of microorganisms. This study aimed to identify and investigate the role of Triticum durum PDFs (TdPDFs) in response to environmental stresses. Prior to this, in silico analyses of TdPDF genes were conducted to assess their chromosomal locations, conserved motifs, exon-intron distribution, and cis-regulatory elements in the promoter regions. Additionally, bioinformatic analyses were performed to characterize the structure of TdPDF proteins, evaluate their phylogenetic relationships, predict their subcellular localization, and estimate their physicochemical properties. Docking studies were conducted to assess the interactions between TdPDF proteins and the fungal plasma membrane. A total of 28 TdPDF genes were identified in durum wheat based on their conserved domain PF00304 (gamma-thionin). These genes are distributed across all chromosomes of the durum wheat genome, except for chromosomes 4A and 7A. Analysis of the promoters of these genes revealed numerous elements associated with development, hormone responsiveness, and environmental stress. The majority of TdPDF proteins were predicted to be located extracellular. In addition, TdPDF proteins were classified into three clusters based on sequence similarity. Phylogenetic analysis suggested that TdPDF proteins share ancestral similarities with the PDF sequences of other monocotyledonous species. Molecular docking studies revealed that TdPDF proteins interact with fungal plasma membranes, suggesting that they play a critical role in the resistance of plants to pathogen infections. Expression analysis underlined the crucial role of nine TdPDF genes in the defense responses of durum wheat against both pathogenic and environmental stressors. Overall, our findings underscore the potential of TdPDF genes in host-plant resistance and highlight opportunities for their application in crop improvement toward stress tolerance.

High Nitrogen Enhances Maize Susceptibility to Holotrichia parallela via β-Caryophyllene-Mediated Olfactory Recognition and Jasmonate Suppression

Excessive nitrogen application not only affects plant development but also significantly influences plant-pest interactions. This study investigates how nitrogen fertilization modifies the metabolism of maize (Zea mays) and its interaction with Holotrichia parallela, a key soil-dwelling pest. High-nitrogen (HN) conditions increased the emission of volatile organic compounds (VOCs), with β-caryophyllene and palmitic acid strongly attracting larvae behavior selection, and β-caryophyllene attracting female oviposition. RNA interference targeting HparOR19 and HparOR22 genes confirmed the role of β-caryophyllene in pest olfactory recognition. Conversely, low-nitrogen (LN) conditions stimulated jasmonic acid (JA)-related defenses, while HN promoted the production of primary metabolites such as glucose, fructose, and sucrose, which act as feeding stimulants. These findings highlight the intricate relationship among nitrogen fertilization, maize metabolism, and pest behavior, underscoring the necessity of integrating metabolic insights into effective pest management strategies.

A Stinkbug Salivary Protein Is Indispensable for Insect Feeding and Activates Plant Immunity

Salivary proteins secreted by phytophagous insects play pivotal roles in plant-insect interactions. A salivary protein RpSP27, from the stinkbug Riptortus pedestris, a devastating pest on soybean, was selected for studying due to its ability to induce cell death and activate immune responses in plants. RpSP27 localized to the endoplasmic reticulum and triggered reactive oxygen species burst. Virus-induced gene silencing assays showed RAR1 plays an essential role in RpSP27-induced cell death in Nicotiana benthamiana. Expression analyses revealed that RpSP27 is predominantly expressed in R. pedestris salivary glands. RNA interference-mediated silencing of RpSP27 in R. pedestris significantly reduced insect survival rates and altered feeding behavior by decreasing the formation of salivary sheaths on soybeans and reducing probing and feeding duration. Furthermore, the silencing of RpSP27 in R. pedestris mitigated the staygreen syndrome in soybeans, characterized by delayed senescence and pod abnormalities. This study elucidated the role of RpSP27 in the interaction between R. pedestris and soybean, presenting a potential target for pest management strategies to protect soybean crops from the detrimental effects of R. pedestris feeding.

Transcriptomics integrated with metabolomics reveals the defense response of insect-resistant Zea mays infested with Spodoptera exigua

Maize (Zea mays) is one of the most important cereal crops worldwide. Insect control through host plant resistance plays an important part in improving both yield and quality of maize. Spodoptera exigua is a common insect pest causing destructive damages to maize. To comprehensively understand molecular mechanism of maize defense against S. exigua, integrated transcriptomics and metabolomics analyses were conducted in the insect-resistant maize inbred line CML139 infested with S. exigua for 24 h. 9845 differentially expressed genes and 34 significantly changed metabolites were identified in infested leaves. Maize transcriptional response to S. exigua infestation involved in genes encoding enzymes in biosynthetic process (ribosome, glycerolipid, glycerophospholipid metabolism), genes in valine, leucine and isoleucine degradation, phenylpropanoid pathway and transcription factors. By metabolism analysis, accumulations of amino acids, organic acids, phenylpropanoids and benzoxazinoids (Bxs) were significantly enhanced, with the exception of salicylic acid (SA) and jasmonic acid (JA). The integrated analysis of transcriptomic and metabolic data demonstrated that both transcripts and metabolites involved in phenylpropanoid and Bxs biosynthesis were differentially modulated in S. exigua infested leaves. This study is valuable in understanding the complex mechanism of interaction between plants and insect herbivores and provide a potential strategy to maize pest control.

Fall Armyworm-Induced Secondary Metabolites in Sorghum Defend Against Its Attack

The fall armyworm (FAW), Spodoptera frugiperda, is one of the major agricultural pests that has invaded China. The FAW is a polyphagous insect with the gramineous crop sorghum being a key host plant. However, the basis of sorghum's chemical defense against FAW feeding is still unclear. In this study, we investigated the potential defensive mechanism of sorghum against this insect species. It was found that FAW larvae preferred maize over sorghum, the selection and damage rates for sorghum plants by larvae were significantly lower than those of maize plants, and feeding on sorghum restricted larval weight. The non-target metabolomics revealed that the feeding of FAW larvae altered the plant secondary metabolite spectra in maize and sorghum, resulting in species-specific differential secondary metabolites (DSMs). Of these, 19 DSMs were specific in maize, and 51 in sorghum, and only 6 were found in both species. Two-choice and no-choice feeding assays found that gambogenic acid and chimonanthine, two DSMs unique to sorghum, were found to deter larval feeding and decrease the larval weight. These findings reveal that the defense of sorghum against FAW is regulated by changing the response spectra of secondary metabolites and that the induced metabolites have a defensive function by acting as antifeedants, which provides new insights into employing bioactive plant compounds against polyphagous insects.

Qualitative and Quantitative Analyses of 1-Aminocyclopropane-1-carboxylic Acid Concentrations in Plants Organs Using Phenyl Isothiocyanate Derivatization

1-Aminocyclopropane-1-carboxylic acid (ACC) is a direct precursor of phytohormone ethylene. We used a phenyl isothiocyanate (PITC) derivatization modification method combined with spectrographic analysis to isolate and identify three products of the derivatization reactions of ACC and PITC. The MRM+ mode of UPLC-MS/MS was used to establish the analysis of 6-phenyl-5-thioxo-4,6-diazaspiro[2.4]heptan-7-one (PTH-ACC). Three fragment ions detected at the precursor ion (m/z 219.10) were selected for qualitative analysis (m/z 98.10, 77.15, and 72.10), and the most abundant product ion (m/z 98.10) was selected for quantitative analysis. The conditions for the derivatization reaction for the main product PTH-ACC were analyzed and optimized using response surface methodology, resulting in the optimal derivatization conditions being a reaction temperature of 90 °C, a reaction time of 1.5 h, and a formic acid (FA) concentration of 40%. ACC concentrations in 25-200 mg rice samples was successfully determined. Moreover, the ACC concentrations in the shoots, seeds, and roots of rice, maize, and cotton seedlings were all analyzed. The ACC concentrations were found to exhibit tissue specificity. Interestingly, during the ripening process in tomato and mango fruits, the concentrations of ACC in the fruits showed an initial increase, followed by a decrease. In black nightshade fruits, ACC content was the highest in the immature stage, decreased with fruit ripening, and remained stable from the semimature to mature stages. These results provide a reliable analysis technology foundation for the study of ethylene.

A Fungal Endophyte Alters Poplar Leaf Chemistry, Deters Insect Feeding and Shapes Insect Community Assembly

Fungal endophytes of grasses and other herbaceous plants have been known to provide plants with anti-herbivore defence compounds, but there is little information about whether the endophytes of trees also engage in such mutualisms. We investigated the influence of the endophytic fungus Cladosporium sp. on the chemical defences of black poplar (Populus nigra) trees and the consequences for feeding preference and fitness of herbivorous insects and insect community assembly. Endophyte colonisation increased both constitutive- and induced poplar defences. Generalist Lymantria dispar larvae preferred and performed better on uninfected over endophyte-infected poplar leaves, most likely due to higher concentrations of salicinoids in endophyte-inoculated leaves and the endophyte-produced alkaloid stachydrine. Under field conditions, the endophytic fungus shapes insect community assembly i. a. attracting aphids, which can excrete stachydrine. Our results show that endophytic fungi play a crucial role in the defence against insects from different feeding guilds and thereby structuring insect communities.

Comparative translational reprogramming of Glycine max during mechanical wounding

Glycine max (soybean) is a highly protein-rich legume that also contains oils and vitamins. Unfortunately, soybean faces many biotic and abiotic stresses including heat, drought, pests, wounds, infections, and salinity, which limits the crop productivity. Among these, mechanical wounding (MW) causes significant harm to plants, creates a passage for invading pathogens, and disrupts plant metabolism. Thus, exploring soybean responses at the molecular and biochemical levels during mechanical damage is essential. Additionally, MW resembles insect bites, which offers important insights into the immune systems identical to MW and pest attacks. In this investigation, we executed a comparative proteome evaluation of the PUSA9712 soybean variety following MW. Based on specifications of log2FC ≥ 1 and p-value ≤ 0.05, the study disclosed 786 differentially abundant proteins (DAPs) upon MW, among which 294 were elevated and 492 were down-regulated. The function annotation and pathway analysis of DAPs displayed their role in ROS signaling, flavonoid biosynthesis, ABA synthesis, JA-synthesis, defense against pathogens, fatty acid synthesis, brassinosteroid (BR) signaling, carbohydrate metabolism, proteolysis, calcium signaling, and protein kinase pathway. Lipoxygenase, V-type ATPases, Annexin, NsLTP, and ATP-dependent Clp protease proteolytic subunit DAPs can be promising candidates to strengthen soybean crop's resilience to mechanical damage and pest/pathogen attacks and need further functional characterisation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-025-01562-w.

Nymphal feeding suppresses oviposition-induced indirect plant defense in rice

Feeding and oviposition by phytophagous insects are both known to trigger defenses in plants. Whether these two defenses functionally interact remains poorly studied, although these interactions are likely important for pests with overlapping generations. Here we investigated the differences and interaction between feeding- and oviposition-induced plant defenses triggered by the brown planthopper (BPH, Nilaparvata lugens), which gregariously feeds and oviposits on rice. Analyses of host-plant transcriptomes, phytohormones, and direct and indirect defense compounds all show that BPH gravid females (GFs), but not nymphs and non-gravid females (NFs), strongly induce rice defenses. BPH nymphs and GFs prefer to feed on plants previously infested by nymphs over un-attacked plants, but are repelled by plants previously infested by GFs. Moreover, nymph feeding is found to reduce the attractiveness of rice plants to natural enemies and decrease egg parasitism by suppressing GF-induced volatiles that mediate indirect defenses in both growth chambers and paddies. Intergenerational interactions between oviposition- and feeding-induced plant defenses not only promote the development of the population of pest insects but may also contribute to the aggregation behavior of pest insects by suppressing oviposition-induced indirect plant defenses.

Plant Volatile Methyl Salicylate Primes Wheat Defense Against the Grain Aphid by Altering the Synthesis of Defense Metabolites

Wheat (Triticum aestivum L.) is one of the most important staple crops all over the world. Its productivity is adversely affected by aphid infestation. Plant volatiles play a critical role in plant communication, inducing direct and indirect defenses against insect pests. However, little is known about the priming mechanism of key volatiles in wheat. To determine whether and how plant volatile induced defense priming in wheat against the grain aphid Sitobion avenae, a combination of insect bioassays, phytohormone and defense metabolite quantification, and transcriptome analyses were performed using an important aphid damage-induced plant volatile, methyl salicylate (MeSA). MeSA treatment primed wheat for enhanced accumulation of salicylic acid, flavonoid and benzoxazinoids (BXs), and increased resistance to S. avenae and attractiveness to an aphid parasitoid Aphelinus asychis. Supplementation with a BX (2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one) and two flavonoids (xanthohumol and isobavachalcone) in artificial diet impaired the survival, development and fecundity of S. avenae. Moreover, MeSA treatment induced wheat volatile emission especially MeSA. Functional investigation of odorant-binding proteins (OBPs) in A. asychis revealed that AasyOBP4 is responsible for the recognition of MeSA. Taken together, our results provide insights into the molecular mechanism of MeSA-mediated defense in wheat and propose MeSA as a phytoprotectant for crop protection and sustainable agriculture.

HcCYP6AE178 plays a crucial role in facilitating Hyphantria cunea's adaptation to a diverse range of host plants

Strong multi-host adaptability significantly contributes to the rapid dissemination of Hyphantria cunea. The present study explores the involvement of cytochrome P450 monooxygenase (P450) in the multi-host adaptation of H. cunea and aims to develop RNA pesticides targeting essential P450 genes to disrupt this adaptability. The results showed that inhibiting P450 activity notably reduced larval weight and food-intake across seven plants groups. The P450 gene HcCYP6AE178 was highly upregulated in H. cunea larvae from medium- and low-preference host plant groups. Silencing HcCYP6AE178 significantly decreased H. cunea larval body weight, increased larval mortality, inhibited energy metabolism genes expression and interfered with growth regulatory genes expression. Overexpression of HcCYP6AE178 enhanced the tolerance of Drosophila and Sf9 cells to the plant defensive substances cytisine and coumarin. The RNA pesticide CS-dsHcCYP6AE178 constructed using chitosan (CS) exhibited remarkable stability. Treatment with CS-dsHcCYP6AE178 effectively reduced H. cunea larval body weight, heightened larval mortality, and disrupted growth regulatory genes expression in low-preference host plant groups. Combined treatment of CS-dsHcCYP6AE178 and coumarin significantly elevated H. cunea larval mortality compared to coumarin alone, accompanied by the inhibition of growth regulatory genes expression and an abnormal increase in energy metabolism genes expression. Taken together, HcCYP6AE178 is essential for the adaptation of H. cunea to multiple host plants, and RNA pesticides targeting HcCYP6AE178 can effectively impair the performance of H. cunea in different host plants.

AgoArmet and AgoC002: key effector proteins in cotton aphids host adaptation

Aphids are insects that feed on phloem and introduce effector proteins into plant cells through saliva. These effector proteins are key in regulating host plant defense and enhancing aphid host adaptation. We identified these salivary proteins in the cotton aphids genome and named them AgoArmet and AgoC002. Multiple sequence alignment, protein structure analysis, and phylogenetic analysis of these proteins with related proteins from other insects showed that AgoArmet and Armet of Aphis craccivora have high sequence identity (97%) and belong to the same evolutionary branch and that AgoC002 shares the highest sequence identity (80%) and closest evolutionary relationship with C002 of Aphis glyceins. Expression profiling of AgoArmet and AgoC002 showed that they were most highly expressed in cotton aphids during the adult-3d period. Cotton aphids transferred to zucchini leaves resulted in a significant increase in the expression of AgoArmet and AgoC002 within 48h. To investigate the functions of AgoArmet and AgoC002, we decreased the expression of these genes in cotton using virus-induced gene silencing (VIGS), which ultimately led to a 38% and 26% decrease in cotton aphids fecundity, respectively. Moreover, the reduction in AgoC002 expression resulted in a significant (24%) reduction in body weight. Taken together, our findings demonstrate that AgoArmet and AgoC002 are key effector proteins involved in cotton aphids feeding and host adaptation.

Balancing Growth and Defense: Nanoselenium and Melatonin in Tea (Camellia sinensis) Protection against Glufosinate

Current crop stress resistance research suggests that the prominent stimulants nanoselenium (NSe) and melatonin (MT) might improve tea safety, quality, and stress resistance induced by the widely used nonselective herbicide glufosinate (GLU). Their biofortification effects on tea growth, antioxidant activity, and secondary metabolism pathways response to GLU remain unclear. Here, NSe, MT, and their combination NSe-MT effectively reduced 26.6-50.9% GLU and its metabolites in tea seedlings, balanced the photosystem, enhanced antioxidant defenses, and optimized reactive oxygen species scavenging mechanisms. Further, GLU-induced inhibition of glutamine synthetase (11.2-34.0%), ammonium toxicity (55.0-64.7%), and nitrogen metabolism disorders were alleviated. Stimulants exhibited different preferences in the accumulation of l-theanine (8.4-47%), gamma-aminobutyric acid (10.3-41.7%), and catechins (13.1-73.1%, excluding ECG), thereby influencing tea quality. Transcriptomic and metabolomic analyses validated that NSe-MT had a more pronounced impact on tender tea leaves than individual stimulant treatments. All stimulants reduced GLU-induced excessive jasmonic acid (29.8-50.5%) production and signaling responses, revealing their significance in crop physiological activities under herbicide or nitrogen stress. The reduction in aromatic amino acids helped mitigate GLU's interference with phenylpropanoid biosynthesis, leading to inhibited lignin production but enhanced nutritional flavonoid levels, such as catechins. NSe and NSe-MT demonstrated promising potential as herbicide safeners. These findings provided insights into GLU detoxification mechanisms in other nontarget crops as well.

The fall armyworm converts maize endophytes into its own probiotics to detoxify benzoxazinoids and promote caterpillar growth

BACKGROUND

The fall armyworm (FAW, Spodoptera frugiperda) threatens maize production worldwide, and benzoxazinoids (Bxs) are known as the main secondary metabolites produced by maize to defend against FAW. However, we do not yet know whether and in what ways certain endophytes in the digestive system of FAW can metabolize Bxs, thus enhancing the fitness of FAW when feeding on maize.

RESULTS

Using Bxs as the sole carbon and nitrogen source, we isolated Pantoea dispersa from the guts of FAW. P. dispersa can colonize maize roots and leaves as indicated by GFP-labeling and further successfully established itself as an endophyte in the Malpighian tubules and the gut of FAW after FAW feeding activities. Once established, it can be vertically transmitted through FAW eggs, suggesting the potential that FAW can convert maize-derived endophytes into symbiotic bacteria for intergenerational transmission. The prevalence of P. dispersa in FAW guts and maize leaves was also confirmed over large geographic regions, indicating its evolutionary adaptation in fields. Bxs determination in the gut and frass of FAW combined with bioassays performance on maize bx2 mutants revealed that the colonization of P. dispersa can promote FAW growth by metabolizing Bxs rather than other metabolites. Additionally, genome and transcriptome analyses identified plasmid-borne genes, rather than chromosomes of this species, were crucial for Bxs metabolism. This was further validated through in vitro prokaryotic expression assays by expressing two candidate genes form the plasmid.

CONCLUSIONS

FAW can convert maize endophytes into its own probiotics to detoxify Bxs and thus enhance caterpillar growth. This represents a novel strategy for lepidopteran pests-transforming allies of the host into its own-thereby shedding light on the rapid spread of FAW and enhancing our understanding of ecological and evolutionary mechanisms underlying the pest-microbe-plant interactions. Video Abstract.

Mythimna separata herbivory primes Coix resistance in systemic leaves

Coix lacryma-jobi L. belongs to family Poaceae, is widely cultivated in tropical Asian countries for its nutritional and medicinal values. Coix is often threatened by lepidopteran such as Mythimna separata during its life cycle, resulting in severe yield reduction. Insect feeding can trigger defense signaling and increased defense responses in many other crops, yet little is known about whether simulated armyworm feeding on Coix leaves could induce anti-herbivory responses and whether armyworm feeding could activate priming in systemic leaves. In this study, Mythimna separata simulated herbivory elicited increased jasmonic acid (JA) level, JA-Ile (JA-isoleucine conjugate) and altered transcriptome in the Coix leaves. Meanwhile, M. separata simulated herbivory in local leaves primed the systemic leaves for increased accumulation of jasmonic acid and enhanced resistance to M. separata. Consistently, transcriptome analysis showed the systemic leaves were primed, which were up- or down-regulated comparing with the non-primed systemic leaves. In this study, we first reported Mythimna separata simulated herbivory induced increased defense response in leaves of Coix, also Mythimna separata herbivory primed Coix resistance in systemic leaves. This study provides new insight into the regulation of defense responses of Coix against M. separata and the ecological function of priming in Coix.

Construction of a beneficial microbes-enriched rhizosphere system assists plants in phytophagous insect defense: current status, challenges and opportunities

The construction of a plant rhizosphere system enriched with beneficial microbes (BMs) can efficiently help plants defend against phytophagous insects. However, our comprehensive understanding of this approach is still incomplete. In this review, we methodically analyzed the progress made over the last decade, identifying both challenges and opportunities. The main methods for developing a BMs-enriched rhizosphere system include inoculating exogenous BMs into plants, amending the existing soil microbiomes with amendments, and utilizing plants to shape the soil microbiomes. BMs can assist plants in suppressing phytophagous insects across many orders, including 13 Lepidoptera, seven Homoptera, five Hemiptera, five Coleoptera, four Diptera, and one Thysanoptera species by inducing plant systemic resistance, enhancing plant tolerance, augmenting plant secondary metabolite production, and directly suppressing herbivores. Context-dependent factors such as abiotic and biotic conditions, as well as the response of insect herbivores, can affect the outcomes of BM-assisted plant defense. Several challenges and opportunities have emerged, including the development of synthetic microbial communities for herbivore control, the integration of biosensors for effectiveness assessment, the confirmation of BM targets for phytophagous insect defense, and the regulation of outcomes via smart farming with artificial intelligence. This study offers valuable insights for developing a BM-enriched rhizosphere system within an integrated pest management approach. © 2024 Society of Chemical Industry.

Combined transcriptome and metabolome analysis identifies triterpenoid-induced defense responses in Myzus persicae Sülzer-infested peach

Piercing/sucking insects such as green peach aphid (GPA) (Myzus persicae) cause direct damage by obtaining phloem nutrients and indirect damage by spreading plant viruses. To investigate the response of peach trees (Prunus persica) to aphids, the leaf transcriptome and metabolome of two genotypes with different sensitivities to GPA were studied. The gene expression of aphid-susceptible plants infested with aphids was similar to that of control plants, whereas the gene expression of aphid-resistant plants infested with aphids showed strong induced changes in gene expression compared with control plants. Furthermore, gene transcripts in defense-related pathways, including plant-pathogen interaction, MAPK signaling, and several metabolic pathways, were strongly enriched upon aphid infestation. Untargeted secondary metabolite profiling confirmed that aphid infestation induced larger changes in aphid-resistant than in aphid-susceptible peaches. Consistent with transcriptomic alterations, nine triterpenoids showed highly significant GPA-induced accumulation in aphid-resistant peaches, whereas triterpenoid abundance remained predominantly unchanged or undetected in aphid-susceptible peaches. Furthermore, some types of transcription factors (including WRKYs, ERFs, and NACs) were strongly induced upon GPA infestation in aphid-resistant, but not in aphid-susceptible peaches. These results suggested that the accumulation of specialized triterpenoids and the corresponding pathway transcripts may play a key role in peach GPA resistance.

Metabolite profiling and transcriptome analyses reveal defense regulatory network against pink tea mite invasion in tea plant

BACKGROUND

The tea plant Camellia sinensis (L.) O. Kuntze is a perennial crop, invaded by diversity of insect pest species, and pink tea mite is one of the most devastating pests for sustainable tea production. However, molecular mechanism of defense responses against pink tea mites in tea is still unknown. In this study, metabolomics and transcriptome profiles of susceptible and resistant tea varieties were compared before and after pink tea mite infestation.

RESULTS

Metabolomics analysis revealed that abundance levels of polyphenol-related compounds changed significantly before and after infestation. At the transcript level, nearly 8 GB of clean reads were obtained from each sequenced library, and a comparison of infested plants of resistant and susceptible tea varieties revealed 9402 genes with significant differential expression. An array of genes enriched in plant pathogen interaction and biosynthetic pathways of phenylpropanoids showed significant differential regulation in response to pink tea mite invasion. In particular, the functional network linkage of disease resistant proteins, phenylalanine ammonia lyase, flavanone -3-hydroxylase, hydroxycinnamoyl-CoA shikimate transferase, brassinosteroid-6-oxidase 1, and gibberellin 2 beta-dioxygenase induced dynamic defense signals to suppress prolonged pink tea mite attacks. Further integrated analyses identified a complex network of transcripts and metabolites interlinked with precursors of various flavonoids that are likely modulate resistance against to pink tea mite.

CONCLUSIONS

Our results characterized the profiles of insect induced metabolic and transcript reprogramming and identified a defense regulatory network that can potentially be used to fend off pink tea mites damage.

The molecular dynamics between reactive oxygen species (ROS), reactive nitrogen species (RNS) and phytohormones in plant's response to biotic stress

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are critical for plant development as well as for its stress response. They can function as signaling molecules to orchestrate a well-defined response of plants to biotic stress. These responses are further fine-tuned by phytohormones, such as salicylic acid, jasmonic acid, and ethylene, to modulate immune response. In the past decades, the intricacies of redox and phytohormonal signaling have been uncovered during plant-pathogen interactions. This review explores the dynamic interplay of these components, elucidating their roles in perceiving biotic threats and shaping the plant's defense strategy. Molecular regulators and sites of oxidative burst have been explored during pathogen perception. Further, the interplay between various components of redox and phytohormonal signaling has been explored during bacterial, fungal, viral, and nematode infections as well as during insect pest infestation. Understanding these interactions highlights gaps in the current knowledge and provides insights into engineering crop varieties with enhanced resistance to pathogens and pests. This review also highlights potential applications of manipulating regulators of redox signaling to bolster plant immunity and ensure global food security. Future research should explore regulators of these signaling pathways as potential target to develop biotic stress-tolerant crops. Further insights are also needed into roles of endophytes and host microbiome modulating host ROS and RNS pool for exploiting them as biocontrol agents imparting resistance against pathogens in plants.

Comprehensive Transcriptomic Analysis Reveals Defense-Related Genes and Pathways of Rice Plants in Response to Fall Armyworm (Spodoptera frugiperda) Infestation

Rice (Oryza sativa L.) serves as a substitute for bread and is a staple food for half of the world's population, but it is heavily affected by insect pests. The fall armyworm (Spodoptera frugiperda) is a highly destructive pest, threatening rice and other crops in tropical regions. Despite its significance, little is known about the molecular mechanisms underlying rice's response to fall armyworm infestation. In this study, we used transcriptome analysis to explore the global changes in gene expression in rice leaves during a 1 h and 12 h fall armyworm feeding. The results reveal 2695 and 6264 differentially expressed genes (DEGs) at 1 and 12 h post-infestation, respectively. Gene Ontology (GO) and KEGG enrichment analyses provide insights into biological processes and pathways affected by fall armyworm feeding. Key genes associated with hormone regulation, defense metabolic pathways, and antioxidant and detoxification processes were upregulated, suggesting the involvement of jasmonic acid (JA) signaling, salicylic acid biosynthesis pathways, auxin response, and heat shock proteins in defense during 1 h and 12 h after fall armyworm infestation. Similarly, key genes involved in transcriptional regulation and defense mechanisms reveal the activation of calmodulins, transcription factors (TFs), and genes related to secondary metabolite biosynthesis. Additionally, MYB, WRKY, and ethylene-responsive factors (ERFs) are identified as crucial TF families in rice's defense response. This study provides a comprehensive understanding of the molecular dynamics in rice responding to fall armyworm infestation, offering valuable insights for developing pest-resistant rice varieties and enhancing global food security. The identified genes and pathways provide an extensive array of genomic resources that can be used for further genetic investigation into rice herbivore resistance. This also suggests that rice plants may have evolved strategies against herbivorous insects. It also lays the groundwork for novel pest-resistance techniques for rice.

Integrative Omics Strategies for Understanding and Combating Brown Planthopper Virulence in Rice Production: A Review

The brown planthopper (Nilaparvata lugens, BPH) is a serious insect pest responsible for causing immense economic losses to rice growers around the globe. The development of high-throughput sequencing technologies has significantly improved the research on this pest, and its genome structure, gene expression profiles, and host-plant interactions are being unveiled. The integration of genomic sequencing, transcriptomics, proteomics, and metabolomics has greatly increased our understanding of the biological characteristics of planthoppers, which will benefit the identification of resistant rice varieties and strategies for their control. Strategies like more optimal genome assembly and single-cell RNA-seq help to update our knowledge of gene control structure and cell type-specific usage, shedding light on how planthoppers adjust as well. However, to date, a comprehensive genome-wide investigation of the genetic interactions and population dynamics of BPHs has yet to be exhaustively performed using these next-generation omics technologies. This review summarizes the recent advances and new perspectives regarding the use of omics data for the BPH, with specific emphasis on the integration of both fields to help develop more sustainable pest management strategies. These findings, in combination with those of post-transcriptional and translational modifications involving non-coding RNAs as well as epigenetic variations, further detail intricate host-brown planthopper interaction dynamics, especially regarding resistant rice varieties. Finally, the symbiogenesis of the symbiotic microbial community in a planthopper can be characterized through metagenomic approaches, and its importance in enhancing virulence traits would offer novel opportunities for plant protection by manipulating host-microbe interactions. The concerted diverse omics approaches collectively identified the holistic and complex mechanisms of virulence variation in BPHs, which enables efficient deployment into rice resistance breeding as well as sustainable pest management.

Using salicylic acid-responsive promoters to drive the expression of jasmonic acid-regulated genes enhances plant resistance to whiteflies

BACKGROUND

Jasmonic acid (JA) is an important phytohormone used to defend against herbivores, but it does not respond to whitefly feeding. Conversely, another phytohormone, salicylic acid (SA), is induced when plants are fed upon by whiteflies. JA has a better anti-whitefly effect than SA; however, there is limited research on how to effectively improve plant resistance by utilizing the different responses of these phytohormones to whitefly feeding.

RESULTS

We discovered that protease inhibitors 8 (PI8) and terpene synthase 10 (TPS10) located downstream of the JA-regulated pathway in plants have anti-whitefly effects, but these two genes were not induced by whitefly feeding. To identify whitefly-inducible promoters, we compared the transcriptome data of tobacco fed upon by Bemisia tabaci with the control. We focused on pathogenesis-related (PR) genes because they are known to be induced by SA. Among these PR genes, we found that expression levels of pathogenes-related protein 1C-like (PR1) and glucose endo-1,3-beta-glucosidase (BGL) can be significantly induced by whitefly feeding and regulated by SA. We then engineered the whitefly-inducible promoters of BGL and PR1 to drive the expression of PI8 and TPS10. We found that compared with control plants that did not induce the expression of PI8 or TPS10, transformed plants expressing PI8 or TPS10 under the PR1 or BGL promoter showed a significant increase in the expression levels of PI8 and TPS10 after whitefly infection, significantly improving their resistance to whiteflies.

CONCLUSION

Our findings suggest that using SA-inducible promoters as tools to drive the expression of JA-regulated defense genes can enhance plant resistance to whiteflies. Our study provides a novel pathway for the enhancement of plant resistance against insects. © 2024 Society of Chemical Industry.

Transcriptomic and metabolomic analysis of poplar response to feeding by Hyphantria cunea

Populus cathayana × canadansis 'Xinlin 1' ('P.'xin lin 1') with the characteristics of rapid growth and high yield, is frequently attacked by herbivorous insects. However, little is known about how it defenses against Hyphantria cunea (H. cunea) at molecular and biochemical levels. Differences in the transcriptome and metabolome were analyzed after 'P. 'xin lin 1' leaves were fed to H. cunea for 0h, 2h, 4h, 8h, 16h and 24h. In the five comparison groups including 2h vs. CK, 4h vs. CK, 8h vs. CK, 16h vs. CK, and 24h vs. CK, a total of 8925 genes and 842 metabolites were differentially expressed. A total of 825 transcription factors (TFs) were identified, which encoded 56 TF families. The results showed that the top four families with the highest number of TFs were AP2/ERF, MYB, C2C2, bHLH. Analyses of leaves which were fed to H. cunea showed that the differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) were significantly enriched in plant hormone signal transduction pathway, MAPK signaling pathway, flavonoid, flavone and flavonol and anthocyanin biosynthesis pathway. Additionally, there were a number of genes significantly up-regulated in MAPK signaling pathway. Some compounds involved in plant hormone signal transduction and flavonoid/flavone and flavonol/ anthocyanin pathways such as jasmonic acid (JA), jasmonoyl-L-Isoleucine (JA-Ile), kaempferol and cyanidin-3-O-glucoside were induced in infested 'P.'xin lin 1'. This study provides a new understanding for exploring the dynamic response mechanism of poplar to the infestation of H. cunea.

Defense of cabbages against herbivore cutworm Spodoptera litura under Cd stress and insect herbivory stress simultaneously

Biotic (e.g., heavy metal) and abiotic stress (e.g., insect attack) can affect plant chemical defense, but little is known about the changes in plant defense when they occur concurrently. Herein, the impacts of heavy metal cadmium (Cd) stress and insect herbivory stress on the direct and indirect defense of two cultivar cabbages of Brassica campestris, the low-Cd cultivar Lvbao701 and the high-Cd cultivar Chicaixin No.4, against the herbivore cutworm Spodoptera litura were investigated. Although 10 mg kg-1 Cd stress alone inhibited leaf secondary metabolites (total phenolics, flavonoids), it reduced the feeding rate and odor selection of S. litura towards both cultivar cabbages, especially for Lvbao701, by increasing leaf Cd content and repellent volatile organic compounds (VOCs) (6-methyl-5-hepten-2-one, 7,9-di-tert-butyl-1-oxaspiro (4,5)deca-6,9-diene-2,8-dione), and reducing soluble sugar and attractive VOCs (3-methyl-3-pentanol, 2,5-hexanedione, tetradecanal). Under 2.5 mg kg-1 Cd and herbivory stress, although leaf total phenolics and flavonoids increased significantly, the feeding rate and odor selection of S. litura towards both cultivar cabbages increased, especially for Chicaixin No.4, indicating that the chemical defense of cabbages was depressed. Therefore, Cd stress alone improved the insect resistance of cabbages, whereas herbivory stress weakened the enhanced cabbages defence by Cd stress. The low-Cd cultivar Lvbao701 presented stronger insect resistance than Chicaixin No.4, suggesting that Lvbao701 application in Cd-polluted soil can not only decrease Cd transmission to higher levels in the food chain but also reduce pest occurrence.

Secret Weapon of Insects: The Oral Secretion Cocktail and Its Modulation of Host Immunity

Plants and insects have co-existed for almost 400 million years and their interactions can be beneficial or harmful, thus reflecting their intricate co-evolutionary dynamics. Many herbivorous arthropods cause tremendous crop loss, impacting the agro-economy worldwide. Plants possess an arsenal of chemical defenses that comprise diverse secondary metabolites that help protect against harmful herbivorous arthropods. In response, the strategies that herbivores use to cope with plant defenses can be behavioral, or molecular and/or biochemical of which salivary secretions are a key determinant. Insect salivary secretions/oral secretions (OSs) play a crucial role in plant immunity as they contain several biologically active elicitors and effector proteins that modulate plants' defense responses. Using this oral secretion cocktail, insects overcome plant natural defenses to allow successful feeding. However, a lack of knowledge of the nature of the signals present in oral secretion cocktails has resulted in reduced mechanistic knowledge of their cellular perception. In this review, we discuss the latest knowledge on herbivore oral secretion derived elicitors and effectors and various mechanisms involved in plant defense modulation. Identification of novel herbivore-released molecules and their plant targets should pave the way for understanding the intricate strategies employed by both herbivorous arthropods and plants in their interactions.

Scavenging H2O2 of plant host by saliva catalase of leafhopper vector benefits viral transmission

Catalase (CAT) is the main reactive oxygen species (ROS)-scavenging enzyme in plants and insects. However, it remains elusive whether and how insect saliva CAT suppresses ROS-mediated plant defense, thereby promoting initial virus transmission by insect vectors. Here, we investigated how leafhopper Recilia dorsalis catalase (RdCAT) was secreted from insect salivary glands into rice phloem, and how it was perceived by rice chaperone NO CATALASE ACTIVITY1 (OsNCA1) to scavenge excessive H2O2 during insect-to-plant virus transmission. We found that the interaction of OsNCA1 with RdCAT activated its enzymatic activity to decompose H2O2 in rice plants during leafhopper feeding. However, initial insect feeding did not significantly change rice CATs transcripts. Knockout of OsNCA1 in transgenic lines decreased leafhopper feeding-activated CAT activity and caused higher H2O2 accumulation. A devastating rice reovirus activated RdCAT expression and promoted the cosecretion of virions and RdCAT into leafhopper salivary cavities and ultimately into the phloem. Virus-mediated increase of RdCAT secretion suppressed excessive H2O2, thereby promoting host attractiveness to insect vectors and initial virus transmission. Our findings provide insights into how insect saliva CAT is secreted and perceived by plant chaperones to suppress the early H2O2 burst during insect feeding, thereby facilitating viral transmission.

Temporal transcriptome and metabolome study revealed molecular mechanisms underlying rose responses to red spider mite infestation and predatory mite antagonism

Introduction

Red spider mite (Tetranychus urticae) infestation (SMI) is a detrimental factor for roses grown indoors. Although predatory mite (Neoseiulus californicus) antagonism (PMA) is often utilized to alleviate SMI damage, little is known about the defensive response of greenhouse-grown roses to SMI and the molecular mechanism by which PMA protects roses.

Methods

To determine the transcriptome and metabolome responses of roses to SMI and PMA, the leaves of a rose cultivar ("Fairy Zixia/Nightingale") were infested with T. urticae, followed by the introduction of predator mite. Leaf samples were collected at various time points and subjected to transcriptome and metabolome analyses.

Results

We found that 24 h of SMI exerted the most changes in the expression of defense-related genes and metabolites in rose leaves. KEGG pathway analysis of differentially expressed genes (DEGs) and metabolites revealed that rose responses to SMI and PMA were primarily enriched in pathways such as sesquiterpenoid and triterpenoid biosynthesis, benzoxazinoid biosynthesis, stilbenoid, diarylheptanoid and gingerol biosynthesis, phytosterol biosynthesis, MAPK signaling pathway, phenylpropanoid biosynthesis, and other pathways associated with resistance to biotic stress. Rose reacted to SMI and PMA by increasing the expression of structural genes and metabolite levels in phytosterol biosynthesis, mevalonate (MVA) pathway, benzoxazinoid biosynthesis, and stilbenoid biosynthesis. In addition, PMA caused a progressive recover from SMI, allowing rose to revert to its normal growth state. PMA restored the expression of 190 essential genes damaged by SMI in rose leaves, including transcription factors DRE1C, BH035, MYB14, EF110, WRKY24, NAC71, and MY108. However, after 144 h of PMA treatment, rose responsiveness to stimulation was diminished, and after 192 h, the metabolic levels of organic acids and lipids were recovered in large measure.

Conclusion

In conclusion, our results offered insights on how roses coordinate their transcriptome and metabolome to react to SMI and PMA, therefore shedding light on how roses, T. urticae, and N. californicus interact.

Effector enrichment by Candidatus Liberibacter promotes Diaphorina citri feeding via Jasmonic acid pathway suppression

BACKGROUND

Citrus huanglongbing (HLB) is a devastating disease caused by Candidatus Liberibacter asiaticus (CLas) that affects the citrus industry. In nature, CLas relies primarily on Diaphorina citri Kuwayama as its vector for dissemination. After D. citri ingests CLas-infected citrus, the pathogen infiltrates the insect's body, where it thrives, reproduces, and exerts regulatory control over the growth and metabolism of D. citri. Previous studies have shown that CLas alters the composition of proteins in the saliva of D. citri, but the functions of these proteins remain largely unknown.

RESULTS

In this study, we detected two proteins (DcitSGP1 and DcitSGP3) with high expression levels in CLas-infected D. citri. Quantitative PCR and Western blotting analysis showed that the two proteins were highly expressed in the salivary glands and delivered into the host plant during feeding. Silencing the two genes significantly decreased the survival rate for D. citri, reduced phloem nutrition sucking and promoted jasmonic acid (JA) defenses in citrus. By contrast, after overexpressing the two genes in citrus, the expression levels of JA pathway-associated genes decreased.

CONCLUSION

Our results suggest that CLas can indirectly suppress the defenses of citrus and support feeding by D. citri via increasing the levels of effectors in the insect's saliva. This discovery facilitates further research into the interaction between insect vectors and pathogens. © 2024 Society of Chemical Industry.

Comparative proteome analysis of Spodoptera litura-infested Zea mays reveals a robust defense strategy targeting insect peritrophic membrane

Herbivorous insects such as Spodoptera litura, pose a constant threat to agricultural crops. The incompetence of contemporary pest management tools and techniques stipulates unravelling of molecular dogma, that drives pest-plant interaction. From our previous observations, we inferred that despite being a voracious polyphagous herbivore, S. litura growth and adaptability is severely hampered on maize foliage diet. In this investigation we explored further and demonstrated the impact of maize diet on the insect gut peritrophic membrane (PM, a crucial membrane involved in compartmentalizing digestive events and absorption of nutrients), its structural analysis using scanning electron microscopy (SEM) revealed damaged and perforated PM. Further, this study delves into the intricate resistance mechanism adapted by Z. mays against S. litura by conducting a comparative proteome analysis. We have detected 345 differentially abundant proteins (DAPs) at p < 0.05 and fold change ≥1. The DAPs were categorized as plant defense, secondary metabolite synthesis, redox homeostasis, cytoskeleton/cell wall biosynthesis, primary metabolism, transport and molecular processes. We remarkably report differential expression of proteolysis- and defense-related proteins that have potential to target insect gut, digestion and absorption of nutrients. Our findings contribute to a deeper understanding of the molecular dynamics governing maize resistance against S. litura. Understanding of such intricate molecular dialogues at these interfaces could provide valuable information on the arms race between plants and herbivores, it may pave the way for innovative pest management strategies.

Egg-associated secretions from the brown planthopper (Nilaparvata lugens) activate rice immune responses

The brown planthopper (BPH, Nilaparvata lugens) is a notorious sap-sucking insect pest that damages rice (Oryza sativa) plants throughout Asia. During BPH feeding, saliva enters rice plant tissues, whereas during oviposition egg-associated secretions (EAS) are deposited in damaged plant tissue. Dynamic changes in rice to planthopper salivary effectors have been widely reported. However, the effects of EAS from planthopper on rice immunity remains largely unexplored. In this study, we found that both infestation of rice by gravid BPH female adults and treatment with the EAS elicited a strong and rapid accumulation of jasmonic acid (JA), JA-isoleucine, and hydrogen peroxide in rice. EAS enhanced plant defenses not only in rice but also in tobacco, and these impaired the performance of BPH on rice, as well as the performance of aphids and whiteflies on tobacco. High-throughput proteome sequencing of EAS led to 110 proteins being identified and 53 proteins with 2 or more unique peptides being detected. Some proteins from BPH EAS were also found in the salivary proteome from herbivores, suggesting potential evolutionary conservation of effector functions across feeding and oviposition; however, others were only identified in EAS, and these are likely specifically related to oviposition. These findings point to novel proteins affecting interactions between planthoppers and rice during oviposition, providing an additional source of information for effector studies.

Microbial Volatile Organic Compounds: Insights into Plant Defense

Volatile organic compounds (VOCs) are low molecular weight molecules that tend to evaporate easily at room temperature because of their low boiling points. VOCs are emitted by all organisms; therefore, inter- and intra-kingdom interactions have been established, which are fundamental to the structuring of life on our planet. One of the most studied interactions through VOCs is between microorganism VOCs (mVOCs) and plants, including those of agricultural interest. The mVOC interactions generate various advantages for plants, ranging from promoting growth to the activation of defense pathways triggered by salicylic acid (systemic acquired resistance) and jasmonic acid (induced systemic resistance) to protect them against phytopathogens. Additionally, mVOCs directly inhibit the growth of phytopathogens, thereby providing indirect protection to plants. Among the current agricultural problems is the extensive use of chemicals, such as fertilizers, intended to combat production loss, and pesticides to combat phytopathogen infection. This causes problems in food safety and environmental pollution. Therefore, to overcome this problem, it is important to identify alternatives that do not generate environmental impacts, such as the application of mVOCs. This review addresses the protective effects of mVOCs emitted by microorganisms from different kingdoms and their implications in plant defense pathways.

An effector of Phthorimaea absoluta oral secretions inhibits host plant defense

Insects have evolved effectors to regulate host defenses for efficient feeding, yet their impact on chewing insects, like the tomato leaf miner (Phthorimaea absoluta), a significant pest, is poorly understood. We used RNAi to target the REPAT38 gene in larvae, monitoring changes at 0.5, 1, 2, and 4 h in leaf stomata, plant hormone concentrations (jasmonic acid (JA), jasmonoyl-L-isoleucine (JA-Ile), salicylic acid (SA), ethylene (ET), and abscisic acid (ABA)), and 12 hormone-responsive genes to explore the molecular mechanism of REPAT38-mediated plant-insect interactions. The results showed that the effector induced stomatal closure at 0.5 h and inhibited the synthesis of JA, ET, and ABA at 1 h. Additionally, seven plant hormone-responsive genes-AOC, MYC2, ACS1A, PAL, PR1, EIL2, and SRK2E-were inhibited at various time points. Our data suggest that REPAT38, as an effector with conserved functions, can weaken tomato host defenses and conducive to insect adaptation to host plants.

Heat stress reprograms herbivory-induced defense responses in potato plants

Climate change is predicted to increase the occurrence of extreme weather events such as heatwaves, which may thereby impact the outcome of plant-herbivore interactions. While elevated temperature is known to directly affect herbivore growth, it remains largely unclear if it indirectly influences herbivore performance by affecting the host plant they feed on. In this study, we investigated how transient exposure to high temperature influences plant herbivory-induced defenses at the transcript and metabolic level. To this end, we studied the interaction between potato (Solanum tuberosum) plants and the larvae of the potato tuber moth (Phthorimaea operculella) under different temperature regimes. We found that P. operculella larvae grew heavier on leaves co-stressed by high temperature and insect herbivory than on leaves pre-stressed by herbivory alone. We also observed that high temperature treatments altered phylotranscriptomic patterns upon herbivory, which changed from an evolutionary hourglass pattern, in which transcriptomic responses at early and late time points after elicitation are more variable than the ones in the middle, to a vase pattern. Specifically, transcripts of many herbivory-induced genes in the early and late defense stage were suppressed by HT treatment, whereas those in the intermediate stage peaked earlier. Additionally, we observed that high temperature impaired the induction of jasmonates and defense compounds upon herbivory. Moreover, using jasmonate-reduced (JA-reduced, irAOC) and -elevated (JA-Ile-elevated, irCYP94B3s) potato plants, we showed that high temperature suppresses JA signaling mediated plant-induced defense to herbivore attack. Thus, our study provides evidences on how temperature reprograms plant-induced defense to herbivores.

Salicylic acid positively regulates maize defenses against lepidopteran insects

In response to insect attack, plants use intricate signaling pathways, including phytohormones, such as jasmonate (JA), ethylene (ET), and salicylic acid (SA), to activate defenses. Maize (Zea mays) is one of the most important staple food crops around the world. Previous studies have shown that the JA and ET signaling play important roles in maize defense against insects, but little is known about whether and how SA regulates maize resistance to insect herbivores. In this study, we ectopically expressed the NahG (salicylate hydroxylase) gene in maize plants (NahG maize) to block the accumulation of SA. It was found that compared with the wild-type (WT) maize, the NahG maize exhibited decreased resistance to the generalist insects S podoptera litura and Spodoptera frugiperda and the specialist Mythimna separata, and the compromised resistance in the NahG maize was associated with decreased levels of defensive metabolites benzoxazinoids (Bxs) and chlorogenic acid (CA). Quantification of simulated S. litura feeding-induced JA, JA-isoleucine conjugate (JA-Ile), and ET in the WT and NahG maize indicated that SA does not regulate JA or JA-Ile, but positively controls ET. We provide evidence suggesting that the SA pathway does not crosstalk with the JA or the ET signaling in regulating the accumulation of Bxs and CA. Transcriptome analysis revealed that the bHLH, ERF, and WRKY transcription factors might be involved in SA-regulated defenses. This study uncovers a novel and important phytohormone pathway in maize defense against lepidopterous larvae.

Selection of host plants for production of Clanis bilineata (Lepidoptera: Sphingidae)

Clanis bilineata Walker (Lepidoptera: Sphingidae), a burgeoning edible insect, is experiencing rising demand in China and other regions. Despite this interest, larval production is currently constrained by the limitations of artificial production technologies, particularly the selection of optimal host plants. This study rigorously evaluated the performance of C. bilineatha larvae on four main host plants: round-leaf soybean, pointed-leaf soybean, black locust, and kudzu. Preference tests demonstrated that the larvae were most attracted to black locust (34.76 ± 4.65%), with subsequent preferences for kudzu (25.00 ± 6.12%), round-leaf soybean (23.17 ± 2.79%), and pointed-leaf soybean (14.02 ± 4.74%). No significant preference differences were noted between round-leaf soybean and either black locust or kudzu. In feeding assays, the larvae exhibited a marked preference for round-leaf soybean (37.36 ± 0.81 g, total feeding amount for larvae), followed by kudzu (37.26 ± 0.82 g), pointed-leaf soybean (35.38 ± 1.31 g), and black locust (28.53 ± 0.81 g). When the larvae were fed on round-leaf soybean, they exhibited significantly higher survival rate (39.33 ± 0.90%), body weight (9.75 ± 0.07 g), total biomass (383.43 ± 7.35 g), pupation rate (87.78 ± 1.73%), and egg production (189.80 ± 1.06 eggs/female) compared to other hosts. These findings uncovered that round-leaf soybean significantly enhances larval performance, suggesting its potential for improving C. bilineata larval production and sustainability in cultivation systems.

Plant Immunity: At the Crossroads of Pathogen Perception and Defense Response

Plants are challenged by different microbial pathogens that affect their growth and productivity. However, to defend pathogen attack, plants use diverse immune responses, such as pattern-triggered immunity (PTI), effector-triggered immunity (ETI), RNA silencing and autophagy, which are intricate and regulated by diverse signaling cascades. Pattern-recognition receptors (PRRs) and nucleotide-binding leucine-rich repeat (NLR) receptors are the hallmarks of plant innate immunity because they can detect pathogen or related immunogenic signals and trigger series of immune signaling cascades at different cellular compartments. In plants, most commonly, PRRs are receptor-like kinases (RLKs) and receptor-like proteins (RLPs) that function as a first layer of inducible defense. In this review, we provide an update on how plants sense pathogens, microbe-associated molecular patterns (PAMPs or MAMPs), and effectors as a danger signals and activate different immune responses like PTI and ETI. Further, we discuss the role RNA silencing, autophagy, and systemic acquired resistance as a versatile host defense response against pathogens. We also discuss early biochemical signaling events such as calcium (Ca2+), reactive oxygen species (ROS), and hormones that trigger the activation of different plant immune responses. This review also highlights the impact of climate-driven environmental factors on host-pathogen interactions.

A chromosome-scale genome of Rhus chinensis Mill. provides new insights into plant-insect interaction and gallotannins biosynthesis

Rhus chinensis Mill., an economically valuable Anacardiaceae species, is parasitized by the galling aphid Schlechtendalia chinensis, resulting in the formation of the Chinese gallnut (CG). Here, we report a chromosomal-level genome assembly of R. chinensis, with a total size of 389.40 Mb and scaffold N50 of 23.02 Mb. Comparative genomic and transcriptome analysis revealed that the enhanced structure of CG and nutritional metabolism contribute to improving the adaptability of R. chinensis to S. chinensis by supporting CG and galling aphid growth. CG was observed to be abundant in hydrolysable tannins (HT), particularly gallotannin and its isomers. Tandem repeat clusters of dehydroquinate dehydratase/shikimate dehydrogenase (DQD/SDH) and serine carboxypeptidase-like (SCPL) and their homologs involved in HT production were determined as specific to HT-rich species. The functional differentiation of DQD/SDH tandem duplicate genes and the significant contraction in the phenylalanine ammonia-lyase (PAL) gene family contributed to the accumulation of gallic acid and HT while minimizing the production of shikimic acid, flavonoids, and condensed tannins in CG. Furthermore, we identified one UDP glucosyltransferase (UGT84A), three carboxylesterase (CXE), and six SCPL genes from conserved tandem repeat clusters that are involved in gallotannin biosynthesis and hydrolysis in CG. We then constructed a regulatory network of these genes based on co-expression and transcription factor motif analysis. Our findings provide a genomic resource for the exploration of the underlying mechanisms of plant-galling insect interaction and highlight the importance of the functional divergence of tandem duplicate genes in the accumulation of secondary metabolites.

Transcriptomic analysis of the defense response in "Cabernet Sauvignon" grape leaf induced by Apolygus lucorum feeding

To investigate the molecular mechanism of the defense response of "Cabernet Sauvignon" grapes to feeding by Apolygus lucorum, high-throughput sequencing technology was used to analyze the transcriptome of grape leaves under three different treatments: feeding by A. lucorum, puncture injury, and an untreated control. The research findings indicated that the differentially expressed genes were primarily enriched in three aspects: cellular composition, molecular function, and biological process. These genes were found to be involved in 42 metabolic pathways, particularly in plant hormone signaling metabolism, plant-pathogen interaction, MAPK signaling pathway, and other metabolic pathways associated with plant-induced insect resistance. Feeding by A. lucorum stimulated and upregulated a significant number of genes related to jasmonic acid and calcium ion pathways, suggesting their crucial role in the defense molecular mechanism of "Cabernet Sauvignon" grapes. The consistency between the gene expression and transcriptome sequencing results further supports these findings. This study provides a reference for the further exploration of the defense response in "Cabernet Sauvignon" grapes by elucidating the expression of relevant genes during feeding by A. lucorum.

Brevipalpus yothersi Baker (Tenuipalpidae) development in sweet orange plants is influenced by previous mite infestation and the presence of shelters

Citrus leprosis is the most important viral disease affecting citrus. The disease is caused predominantly by CiLV-C and is transmitted by Brevipalpus yothersi Baker mites. This study brings some insight into the colonization of B. yothersi in citrus [(Citrus × sinensis (L.) Osbeck (Rutaceae)] previously infested by viruliferous or non-viruliferous B. yothersi. It also assesses the putative role of shelters on the behavior of B. yothersi. Expression of PR1 and PR4 genes, markers of plant defense mechanisms, were evaluated by RT-qPCR to correlate the role of the plant hormonal changes during the tri-trophic virus-mite-plant interplay. A previous infestation with either non-viruliferous and viruliferous mites positively influenced oviposition and the number of adult individuals in the resulting populations. Mite populations were higher on branches that had received a previous mite infestation than branches that did not. There was an increase in the expression of PR4, a marker gene in the jasmonic acid (JA) pathway, in the treatment with non-viruliferous mites, indicating a response from the plant to their feeding. Conversely, an induced expression of PR1, a marker gene in the salicylic acid (SA) pathway, was observed mainly in the treatment with viruliferous mites, which suggests the activation of a plant response against the pathogen. The earlier mite infestation, as well as the presence of leprosis lesions and a gypsum mixture as artificial shelters, all fostered the growth of the B. yothersi populations after the second infestation, regardless of the presence or absence of CiLV-C. Furthermore, it is suggested that B. yothersi feeding actually induces the JA pathway in plants. At the same time, the CiLV-C represses the JA pathway and induces the SA pathway, which benefits the mite vector.

Identification of two key genes involved in flavonoid catabolism and their different roles in apple resistance to biotic stresses

Biosynthesis of flavonoid aglycones and glycosides is well established. However, key genes involved in their catabolism are poorly understood, even though the products of hydrolysis and oxidation play important roles in plant resistance to biotic stress. Here, we report on catabolism of dihydrochalcones (DHCs), the most abundant flavonoids in domesticated apple and wild Malus. Two key genes, BGLU13.1 and PPO05, were identified by activity-directed protein purification. BGLU13.1-A hydrolyzed phlorizin, (the most abundant DHC in domesticated apple) to produce phloretin which was then oxidized by PPO05. The process differed in some wild Malus, where trilobatin (a positional isomer of phlorizin) was mainly oxidized by PPO05. The effects of DHC catabolism on apple resistance to biotic stresses was investigated using transgenic plants. Either directly or indirectly, phlorizin hydrolysis affected resistance to the phytophagous pest two-spotted spider mite, while oxidation of trilobatin was involved in resistance to the biotrophic fungus Podosphaera leucotricha. DHC catabolism did not affect apple resistance to necrotrophic pathogens Valsa mali and Erwinia amylovara. These results suggest that different DHC catabolism pathways play different roles in apple resistance to biotic stresses. The role of DHC catabolism on apple resistance appeared closely related to the mode of invasion/damage used by pathogen/pest.

Integrated Omics Analysis Reveals Key Pathways in Cotton Defense against Mirid Bug (Adelphocoris suturalis Jakovlev) Feeding

The recent dominance of Adelphocoris suturalis Jakovlev as the primary cotton field pest in Bt-cotton-cultivated areas has generated significant interest in cotton pest control research. This study addresses the limited understanding of cotton defense mechanisms triggered by A. suturalis feeding. Utilizing LC-QTOF-MS, we analyzed cotton metabolomic changes induced by A. suturalis, and identified 496 differential positive ions (374 upregulated, 122 downregulated) across 11 categories, such as terpenoids, alkaloids, phenylpropanoids, flavonoids, isoflavones, etc. Subsequent iTRAQ-LC-MS/MS analysis of the cotton proteome revealed 1569 differential proteins enriched in 35 metabolic pathways. Integrated metabolome and proteome analysis highlighted significant upregulation of 17 (89%) proteases in the α-linolenic acid (ALA) metabolism pathway, concomitant with a significant increase in 14 (88%) associated metabolites. Conversely, 19 (73%) proteases in the fructose and mannose biosynthesis pathway were downregulated, with 7 (27%) upregulated proteases corresponding to the downregulation of 8 pathway-associated metabolites. Expression analysis of key regulators in the ALA pathway, including allene oxidase synthase (AOS), phospholipase A (PLA), allene oxidative cyclase (AOC), and 12-oxophytodienoate reductase3 (OPR3), demonstrated significant responses to A. suturalis feeding. Finally, this study pioneers the exploration of molecular mechanisms in the plant-insect relationship, thereby offering insights into potential novel control strategies against this cotton pest.

Rice physical defenses and their role against insect herbivores

MAIN CONCLUSION

Understanding surface defenses, a relatively unexplored area in rice can provide valuable insight into constitutive and induced defenses against herbivores. Plants have evolved a multi-layered defense system against the wide range of pests that constantly attack them. Physical defenses comprised of trichomes, wax, silica, callose, and lignin, and are considered as the first line of defense against herbivory that can directly affect herbivores by restricting or deterring them. Most studies on physical defenses against insect herbivores have been focused on dicots compared to monocots, although monocots include one of the most important crops, rice, which half of the global population is dependent on as their staple food. In rice, Silica is an important element stimulating plant growth, although Silica has also been found to impart resistance against herbivores. However, other physical defenses in rice including wax, trichomes, callose, and lignin are less explored. A detailed exploration of the morphological structures and functional consequences of physical defense structures in rice can assist in incorporating these resistance traits in plant breeding and genetic improvement programs, and thereby potentially reduce the use of chemicals in the field. This mini review addresses these points with a closer look at current literature and prospects on rice physical defenses.

Identification and characterization of two P450 enzymes from Citrus sinensis involved in TMTT and DMNT biosyntheses and Asian citrus psyllid defense

The homoterpenes (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT) are the major herbivore-induced plant volatiles that help in defense directly by acting as repellants and indirectly by recruiting insects' natural enemies. In this study, DMNT and TMTT were confirmed to be emitted from citrus (Citrus sinensis) leaves infested with Asian citrus psyllid (Diaphorina citri Kuwayama; ACP), and two cytochrome P450 (CYP) genes (CsCYP82L1 and CsCYP82L2) were newly identified and characterized. Understanding the functions of these genes in citrus defense will help plan strategies to manage huanglongbing caused by Candidatus Liberibacter asiaticus (CLas) and spread by ACP. Quantitative real-time PCR (qPCR) analysis showed that CsCYP82L1 and CsCYP82L2 were significantly upregulated in citrus leaves after ACP infestation. Yeast recombinant expression and enzyme assays indicated that CsCYP82L1 and CsCYP82L2 convert (E)-nerolidol to DMNT and (E,E)-geranyllinalool to TMTT. However, citrus calluses stably overexpressing CsCYP82L1 generated only DMNT, whereas those overexpressing CsCYP82L2 produced DMNT and TMTT. Furthermore, ACPs preferred wild-type lemon (Citrus limon) over the CsCYP82L1-overexpressing line in dual-choice feeding assays and mineral oil over TMTT or DMNT in behavioral bioassays. Finally, yeast one-hybrid, electrophoretic mobility shift, and dual luciferase assays demonstrated that CsERF017, an AP2/ERF transcription factor, directly bound to the CCGAC motif and activated CsCYP82L1. Moreover, the transient overexpression of CsERF017 in lemon leaves upregulated CsCYP82L1 in the absence and presence of ACP infestation. These results provide novel insights into homoterpene biosynthesis in C. sinensis and demonstrate the effect of homoterpenes on ACP behavior, laying a foundation to genetically manipulate homoterpene biosynthesis for application in huanglongbing and ACP control.

Primal awareness, evolutionary restriction, life and the origin of quantum mechanics

We consider resemblances between humans and other species, without adopting categorical positions of either anthropomorphism or anti-anthropomorphism. Our target in doing so is to present a basis for the suggestion of a common ancestor for the similar or differing capabilities exhibited by different species. We propose that individual species exhibit a species-specific selection within what we describe as a universally available 'Basic Capacity to Interact with the Environment' (BCIE). We justify this proposition in terms of the ubiquitous presence at all organizational levels of the Universe of a primal awareness - a precursor of Nature. On disassembling natural organic systems - through neurons, biochemistry … down to quantum mechanics, we note that in its suggested position coupling input-to-output in quantum mechanical operations, primal awareness would be the precursor of quantum mechanics itself. We relate ubiquitous primal awareness to the ideas of David Bohm and Charles Peirce. We point out that genetic Evolution not only provides the basis for the implementation of many capabilities through our 'Basic Capacity to Interact with the Environment', but equally excludes numerous others. This then could explain why different species' Evolution fixes their available/unavailable capabilities. Quantum mechanical superposition/coherence/entanglement are related to our universal primal awareness, in its sense as a ubiquitous precursor. We point out that life is dependent on the classical simulation of quantum mechanics.

Integrated transcriptome and DNA methylome analysis reveal the biological base of increased resistance to gray leaf spot and growth inhibition in interspecific grafted tomato scions

BACKGROUND

Grafting is widely used as an important agronomic approach to deal with environmental stresses. However, the molecular mechanism of grafted tomato scions in response to biotic stress and growth regulation has yet to be fully understood.

RESULTS

This study investigated the resistance and growth performance of tomato scions grafted onto various rootstocks. A scion from a gray leaf spot-susceptible tomato cultivar was grafted onto tomato, eggplant, and pepper rootstocks, creating three grafting combinations: one self-grafting of tomato/tomato (TT), and two interspecific graftings, namely tomato/eggplant (TE) and tomato/pepper (TP). The study utilized transcriptome and DNA methylome analyses to explore the regulatory mechanisms behind the resistance and growth traits in the interspecific graftings. Results indicated that interspecific grafting significantly enhanced resistance to gray leaf spot and improved fruit quality, though fruit yield was decreased compared to self-grafting. Transcriptome analysis demonstrated that, compared to self-grafting, interspecific graftings triggered stronger wounding response and endogenous immune pathways, while restricting genes related to cell cycle pathways, especially in the TP grafting. Methylome data revealed that the TP grafting had more hypermethylated regions at CHG (H = A, C, or T) and CHH sites than the TT grafting. Furthermore, the TP grafting exhibited increased methylation levels in cell cycle related genes, such as DNA primase and ligase, while several genes related to defense kinases showed decreased methylation levels. Notably, several kinase transcripts were also confirmed among the rootstock-specific mobile transcripts.

CONCLUSIONS

The study concludes that interspecific grafting alters gene methylation patterns, thereby activating defense responses and inhibiting the cell cycle in tomato scions. This mechanism is crucial in enhancing resistance to gray leaf spot and reducing growth in grafted tomato scions. These findings offer new insights into the genetic and epigenetic contributions to agronomic trait improvements through interspecific grafting.

The WRKY46-MYC2 module plays a critical role in E-2-hexenal-induced anti-herbivore responses by promoting flavonoid accumulation

Volatile organic compounds (VOCs) play key roles in plant-plant communication, especially in response to pest attack. E-2-hexenal is an important component of VOCs, but it is unclear whether it can induce endogenous plant resistance to insects. Here, we show that E-2-hexenal activates early signaling events in Arabidopsis (Arabidopsis thaliana) mesophyll cells, including an H2O2 burst at the plasma membrane, the directed flow of calcium ions, and an increase in cytosolic calcium concentration. Treatment of wild-type Arabidopsis plants with E-2-hexenal increases their resistance when challenged with the diamondback moth Plutella xylostella L., and this phenomenon is largely lost in the wrky46 mutant. Mechanistically, E-2-hexenal induces the expression of WRKY46 and MYC2, and the physical interaction of their encoded proteins was verified by yeast two-hybrid, firefly luciferase complementation imaging, and in vitro pull-down assays. The WRKY46-MYC2 complex directly binds to the promoter of RBOHD to promote its expression, as demonstrated by luciferase reporter, yeast one-hybrid, chromatin immunoprecipitation, and electrophoretic mobility shift assays. This module also positively regulates the expression of E-2-hexenal-induced naringenin biosynthesis genes (TT4 and CHIL) and the accumulation of total flavonoids, thereby modulating plant tolerance to insects. Together, our results highlight an important role for the WRKY46-MYC2 module in the E-2-hexenal-induced defense response of Arabidopsis, providing new insights into the mechanisms by which VOCs trigger plant defense responses.